诀窍是通过引用传递源数组和目标数组。

function flatten_array(&$arr, &$dst) {
    if(!isset($dst) || !is_array($dst)) {
        $dst = array();
    }
    if(!is_array($arr)) {
        $dst[] = $arr;
    } else {
        foreach($arr as &$subject) {
            flatten_array($subject, $dst);
        }
    }
}

$recursive = array('1', array('2','3',array('4',array('5','6')),'7',array(array(array('8'),'9'),'10')));
echo "Recursive: \r\n";
print_r($recursive);
$flat = null;
flatten_array($recursive, $flat);

echo "Flat: \r\n";
print_r($flat);

// If you change line 3 to $dst[] = &$arr; , you won't waste memory,
// since all you're doing is copying references, and imploding the array 
// into a string will be both memory efficient and fast:)

echo "String:\r\n";
echo implode(',',$flat);

如果你想保住你的钥匙，那就是解决办法。

function flatten(array $array) {
    $return = array();
    array_walk_recursive($array, function($value, $key) use (&$return) { $return[$key] = $value; });
    return $return;
}

不幸的是，它只输出最后的嵌套数组，没有中间键。对于下面的例子:

$array = array(
    'sweet' => array(
        'a' => 'apple',
        'b' => 'banana'),
    'sour' => 'lemon'); 
print_r(flatten($fruits));

输出是:

Array
(
    [a] => apple
    [b] => banana
    [sour] => lemon
)

对于php 5.2

function flatten(array $array) {
    $result = array();

    if (is_array($array)) {
        foreach ($array as $k => $v) {
            if (is_array($v)) {
                $result = array_merge($result, flatten($v));
            } else {
                $result[] = $v;
            }
        }
    }

    return $result;
}

我需要用HTML输入格式表示PHP多维数组。

$test = [
    'a' => [
        'b' => [
            'c' => ['a', 'b']
        ]
    ],
    'b' => 'c',
    'c' => [
        'd' => 'e'
    ]
];

$flatten = function ($input, $parent = []) use (&$flatten) {
    $return = [];

    foreach ($input as $k => $v) {
        if (is_array($v)) {
            $return = array_merge($return, $flatten($v, array_merge($parent, [$k])));
        } else {
            if ($parent) {
                $key = implode('][', $parent) . '][' . $k . ']';

                if (substr_count($key, ']') != substr_count($key, '[')) {
                    $key = preg_replace('/\]/', '', $key, 1);
                }
            } else {
                $key = $k;
            }           

            $return[$key] = $v;
        }
    }

    return $return;
};

die(var_dump( $flatten($test) ));

array(4) {
  ["a[b][c][0]"]=>
  string(1) "a"
  ["a[b][c][1]"]=>
  string(1) "b"
  ["b"]=>
  string(1) "c"
  ["c[d]"]=>
  string(1) "e"
}

简单明了的回答。

function flatten_array(array $array)
{
    return iterator_to_array(
         new \RecursiveIteratorIterator(new \RecursiveArrayIterator($array)));
}

用法:

$array = [
    'name' => 'Allen Linatoc',
    'profile' => [
        'age' => 21,
        'favourite_games' => [ 'Call of Duty', 'Titanfall', 'Far Cry' ]
    ]
];

print_r( flatten_array($array) );

输出(在PsySH):

Array
(
    [name] => Allen Linatoc
    [age] => 21
    [0] => Call of Duty
    [1] => Titanfall
    [2] => Far Cry
)

现在就看你怎么处理钥匙了。干杯

编辑(2017-03-01)

引用Nigel Alderton的担忧/问题:

澄清一下，这保留了键(甚至是数字键)，因此具有相同键的值将丢失。例如数组美元= [a, [' b ', ' c ']]成为数组([0]= > b, c[1] = >)。“a”丢失了，因为“b”也有一个键值为0

引用Svish的回答:

只需将false作为第二个参数($use_keys)添加到iterator_to_array调用中

非递归，非基于引用的实现，这可能比基于递归的实现更容易理解。 可以管理任意深度多维数组，不能平化关联数组。 它的工作原理是每个周期将数组压平一层，直到它完全有效。

function array_flatten(): array{
    $result = func_get_args();
    // check all elements of $list are not arrays
    $_is_flat = function (array $list): bool {
        foreach ($list as $val) {
            if (is_array($val)) {
                return false;
            }
        }
        return true;
    };
    do {
        $tmp = [];
        foreach ($result as $val) {
            if (is_array($val)) {
                if (!array_is_list($val)) {
                    throw new \Exception(sprintf("array_flatten can't handle associative arrays: %s", json_encode($val)));
                }
                $tmp = array_merge($tmp, $val);
            } else {
                $tmp[] = $val;
            }
        }
        $result = $tmp;
    } while (!$_is_flat($result));
    return $result;
}

以下是它处理的情况:

assertEquals(array_flatten(1, 2), $expected = [1, 2], 'array_flatten 1a');
assertEquals(array_flatten([1], [2]), $expected = [1, 2], 'array_flatten 1b');
assertEquals(array_flatten([1], [[2], 3]), $expected = [1, 2, 3], 'array_flatten 1c');
assertEquals(array_flatten(1, [2, 3], [4, 5]), $expected = [1, 2, 3, 4, 5], 'array_flatten 2');
assertEquals(array_flatten(2, 3, [4, 5], [6, 7], 8), $expected = [2, 3, 4, 5, 6, 7, 8], 'array_flatten 3');
assertEquals(array_flatten([2, 3, [4, 5], [6, 7], 8]), $expected = [2, 3, 4, 5, 6, 7, 8], 'array_flatten 4');
assertEquals(array_flatten([2, [3, [4, [5]], [6, [7]], 8]]), $expected = [2, 3, 4, 5, 6, 7, 8], 'array_flatten complex');